Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
1999-09-30
2001-02-06
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S800000, C318S801000
Reexamination Certificate
active
06184648
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control apparatus for driving a motor and, more particularly, to a control apparatus for a motor which requires an accurate torque output.
This patent application is based on Japanese Patent Application No. 10-280112, filed Oct. 1, 1998, the entire content of which is incorporated herein by reference.
FIG. 1
shows the general arrangement of an IGBT inverter apparatus.
FIG. 1
shows a power driving apparatus based on vector control with velocity feedback and current feedback control.
As shown in
FIG. 1
, an input velocity reference signal &ohgr;r* and a velocity feedback signal &ohgr;′ calculated by a velocity detector
1
, primary magnetic flux angle calculator
2
, and differentiator
3
are feedback-calculated. The calculation result is converted into a torque reference signal Tr by a velocity controller
4
. A new torque reference signal is calculated by adding the torque reference signal Tr to a torque reference signal Tr* input from a main host apparatus. The calculated torque reference signal is divided by a secondary magnetic flux reference &PHgr;
2
* to obtain a q-axis torque reference signal Iq*.
On the other hand, a field weakening controller
5
and magnetic flux saturation pattern generator
6
are used to calculate a d-axis current reference signal Id* from the velocity feedback signal &ohgr;′. The calculated q-axis torque reference signal Iq* and d-axis current reference signal Id* and d- and q-axis current feedback signals Id′ and Iq′ are feedback-calculated to generate final current reference signals Id* and Iq*, respectively.
The current reference signals Id* and Iq* are output from current controllers
7
and
8
as voltage references Vd* and Vq*, respectively.
A coordinate conversion/PWM conversion device
9
outputs element gate ignition pulse instructions Gu, Gv, and Gw on the basis of the voltage references Vd* and Vq* output from the current controllers
7
and
8
.
On the basis of the element gate trigger pulse instructions Gu, Gv, and Gw output from the coordinate conversion/PWM conversion device
9
, a power converter
10
converts a DC voltage Vdc supplied from a DC current source into a desired AC voltage Vac and outputs the voltage. The power converter
10
supplies a desired current to a motor
11
to drive it.
In the above arrangement, for a d-axis field current Id as a motor field component in vector control, the secondary magnetic flux reference &PHgr;
2
* is calculated in accordance with the velocity feedback signal &ohgr;′ using a certain field pattern in the field weakening controller
5
.
The field pattern in the field weakening controller
5
is determined by the motor connected to the motor control apparatus and set as a fixed value. When a velocity feedback signal &ohgr; having a certain magnitude is input, the field current component Id in the d-axis of the motor is calculated in accordance with the field pattern.
On the basis of a primary magnetic flux angle &thgr;r calculated by the primary magnetic flux angle calculator
2
and a slip angle &thgr;s calculated by vector control, a secondary magnetic flux angle &thgr;o necessary for vector control such as 2-to 3-axis conversion or 3- to 2-axis conversion is obtained. For this reason, calculation of the secondary magnetic flux angle &thgr;o produces a delay.
In the above-described conventional motor control apparatus, in a region where the motor load as the load of the motor control apparatus is low, a motor current vector I
1
in vector control stays close to the d-axis as an excitation current component, as shown in
FIG. 2
, and we have
I
1
=I
d
(1)
When the motor current I
1
stays near the d-axis as the field current component, the ratio of an error component caused by the conversion/calculation delay in the current feedback coordinate converter
13
and coordinate conversion/PWM conversion device
9
in the current feedback loop to the q-axis torque current component signal Iq as the torque component in vector control is high in the low-load mode, resulting in degradation in torque accuracy.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to solve the above problem, and has as its object to provide a motor control apparatus which suppresses degradation in torque accuracy and realizes an accurate and stable torque output.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a motor control apparatus comprising:
a field weakening device for converting a velocity feedback signal obtained from a rotational speed of a motor into a secondary magnetic flux reference signal by using a field pattern;
a field pattern selector for comparing a predetermined signal with a q-axis torque current reference signal obtained on the basis of the secondary magnetic flux reference signal converted by the field weakening device, the velocity feedback signal, a velocity reference signal, and a torque reference signal, and outputting, on the basis of a comparison result, a control signal for switching the field pattern; and
a field pattern storage section for switching, on the basis of the control signal output from the field pattern selector, the field pattern to be used in the field weakening device.
According to this invention, the magnitude of the d-axis field current vector in vector control is changed by switching the field pattern, thereby setting an arbitrary optimum vector as the motor current vector. Hence, coarseness in the torque accuracy due to conversion/calculation delay in the current feedback coordinate converter and coordinate conversion/PWM conversion device in the current feedback loop can be suppressed, and an accurate torque output can be realized.
According to the second aspect of the present invention, there is provided a motor control apparatus according to the first aspect, wherein the field pattern storage section forcibly switches the field pattern to be used in the field weakening device to a flat field pattern.
According to this invention, when the load of the AC motor reaches a desired low region, a flat field pattern is supplied. With this operation, an error in the d-axis current component due to approximation of the saturation pattern is eliminated in the low-load region, and a more accurate and stable torque can be output.
According to the third aspect of the present invention, there is provided a motor control apparatus according to the first aspect, wherein the field pattern storage section further comprises a section for forcibly switching the field pattern in the field weakening device on the basis of a control signal for switching the field pattern, which is input from a main apparatus.
According to this invention, the field pattern is switched by the control signal output from the main apparatus on the basis of the load of the AC motor or running method. For this reason, running torque output can be realized on the basis of the load situation of the AC motor.
According to the fourth aspect of the present invention, there is provided a motor control apparatus according to the first aspect, further comprising a suppressing section for suppressing a rate of change of the secondary magnetic flux reference signal converted by the field weakening device within a predetermined range of the rate of change.
According to this invention, since the rate of change of the secondary magnetic flux reference signal in switching the field pattern is limited within a predetermined range, the field can be smoothly switched.
According to the fifth aspect of the present invention, there is provided a motor control apparatus comprising:
a field weakening device for converting a velocity feedback signal obtained from a rotational speed of a motor into a secondary magnetic flux reference signal by using a field pattern;
a field shift calculator for calculating a shift amount of the field pattern to be used in the field weakening device, on the basis of a q-axis torque current reference signal obtaine
Kato Yoshihito
Yoshikawa Tadamitsu
Foley & Lardner
Kabushiki Kaisha Toshiba
Ro Bentsu
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